1. Technical Field
The present invention relates to an electronic circuit and an electronic device, and more particularly to an electronic circuit, an electronic device, and the like which receive UWB (ultra wide band) signals.
2. Related Art
A circuit which detects an envelope of a received signal and demodulates a baseband signal has been used for a long time, and various types of such a circuit have been developed. The envelope corresponds to line connecting peak values, and is obtained by smoothing absolute values of alternating current components. Also, a method of squaring and smoothing a signal instead of envelope detection has been used for many years, and is currently called “square wave detection” or the like. For example, JP-A-4-170807 discloses a square detection circuit for obtaining squares of signals and a method of amplitude wave detection using the square detection circuit.
Moreover, a receiver conducting envelope detection is used in UWB communication by IR (impulse radio) using no carrier wave (hereinafter referred to as “UWB-IR” communication). This receiver has advantages shown in JP-A-2004-320083 and JP-A-2005-252740. The technologies disclosed in these references use a rectification circuit and an integration circuit to obtain envelope by smoothing absolute values of alternating current components of signals. The operation for detecting an envelope of modulated carrier waves (signals having high frequency and amplitude variable with time) is hereinafter referred to as “envelope detection”. Currently, there is no example of UWB-IR receiver which uses square wave detection.
However, the square detection circuit according to JP-A-4-170807 uses bi-polar transistors, and does not contain MOS transistors appropriate for integrating large-scale circuits. Also, the square characteristics are approximated only when small signals having current variations sufficiently smaller than those of collector current are inputted, and thus errors are produced when large signals are inputted. For using large signals, the power consumption increases. Moreover, the operation speed of the circuit is not high and thus inappropriate for the structure which uses signals having high frequency close to the performance limit of the element like signals used in the UWB-IR communication. It is possible to perform envelope detection after decreasing frequency of signals by frequency conversion. In this case, however, highly accurate phase synchronization is necessary. When phase is not synchronized, errors of carrier wave frequency between transmission and reception are added to envelope of signals as beat. In this case, signals cannot be demodulated by frequency transformation.
Generally, the level of signals received by a receiver is variable according to receiving conditions. When the receiving signal level varies, signal detection by squares promotes the variations. More specifically, since the square detection uses output signals proportional to the square of the receiving signal level, the performance considerably lowers when the receiving signal level is low. Thus, detection of signal envelope by absolute values of signals is more advantageous than detection by squares.
The technologies disclosed in JP-A-2004-320083 and JP-A-2005-252740 detect UWB signals by absolute values of signals. However, both of the methods shown in these references propose only the principle of the UWB-IR communication, and does not show various problems which should be solved for practical use nor solutions for these problems.
Furthermore, the envelope detection circuit provided by the related-art technologies cannot effectively function for high frequency signals (steep and instant pulses) used in the UWB-IR communication.
JP-A-2004-320083 shows an example of circuit structure which includes a calculation amplifying circuit and an envelope detection circuit having PN junction diode. However, it is difficult to make the circuit having PN junction diode into one chip by CMOS semiconductor process, and it is almost impossible in the practical situation to execute full wave rectification for extremely thin pulses used for the UWB-IR communication and detect an envelope thereof.
While the UWB-IR communication uses high frequency close to the limit of element performance, the operable highest speed of the calculation amplifying circuit is only a fraction of the limit frequency of element performance. Thus, the operation speed is absolutely insufficient. Moreover, the related-art full wave rectification circuit does not operate in a preferable condition when input signals are not sufficiently large for the signal level received by the receiver. Furthermore, according to the full wave rectification circuit, it is almost impossible to detect signals having peak value of only several mV obtained by amplifying receiving signals received through an antenna by using a low-noise amplifying circuit disposed before the full wave rectification circuit in a preferable condition. Thus, methods such as increasing the degree of amplification of the low-noise amplifying circuit disposed before the full wave rectification circuit are required, but these methods produce various problems such as high frequency, complication of system, and increase in power consumption.